Add an API to Pause and Resume background offlining requests.

components/offline_pages/background/request_queue_in_memory_store.cc

Index: components/offline_pages/background/request_queue_in_memory_store.cc
diff --git a/components/offline_pages/background/request_queue_in_memory_store.cc b/components/offline_pages/background/request_queue_in_memory_store.cc
index 32219a91616eef459ea08ab4fb7116258f781355..e2622f9f288d7d5c65fcb80cc1500e1c6ca13a01 100644
--- a/components/offline_pages/background/request_queue_in_memory_store.cc
+++ b/components/offline_pages/background/request_queue_in_memory_store.cc
@@ -4,6 +4,7 @@
 
 #include "components/offline_pages/background/request_queue_in_memory_store.h"
 
+#include <algorithm>
 #include <set>
 
 #include "base/bind.h"
@@ -73,6 +74,32 @@ void RequestQueueInMemoryStore::RemoveRequestsByClientId(
       FROM_HERE, base::Bind(callback, true, count));
 }
 
+void RequestQueueInMemoryStore::ChangeRequestsState(
+    const std::vector<int64_t>& request_ids,
+    const SavePageRequest::RequestState new_state,
+    const UpdateCallback& callback) {
+  int count = 0;
+
+  for (int64_t request_id : request_ids) {
+    auto pair = std::find_if(
+        requests_.begin(), requests_.end(),

[fgorski, 2016/08/10 16:00:09]

I don't think lambda is necessary here, as you we are keying the map using
request_id.

See lines 47-51 for equivalent code without <algorithm>

For finding stuff by other fields this code makes sense, thou.

[Pete Williamson, 2016/08/10 21:38:00]

Ah, good catch, I totally forgot what the map was keyed on.  Fixed.

+        [request_id](
+            std::pair<const long, offline_pages::SavePageRequest> pair) {
+          return (request_id == pair.second.request_id());
+        });
+    if (pair != requests_.end()) {
+      ++count;
+      pair->second.set_request_state(new_state);
+    }
+  }
+
+  RequestQueueStore::UpdateStatus status =
+      count > 0 ? UpdateStatus::UPDATED : UpdateStatus::FAILED;

[fgorski, 2016/08/10 16:00:09]

what if there were no items?
Makes me think that our UpdateCallback could be structured more like
DeleteCallback. Please add a TODO in request_queue_store.h for me.

[Pete Williamson, 2016/08/10 21:38:00]

Done.

+
+  base::ThreadTaskRunnerHandle::Get()->PostTask(FROM_HERE,
+                                                base::Bind(callback, status));
+}
+
 void RequestQueueInMemoryStore::Reset(const ResetCallback& callback) {
   requests_.clear();
   base::ThreadTaskRunnerHandle::Get()->PostTask(FROM_HERE,